Glad you got it sorted
The best thing to do if your son wants to play films on his DVD Player, is to get a cheap one from somewhere like Tesco or Sainsbury that will play anything. The trouble with the big brand ones like Sony or Philips is that these companies have a vested interest in the movie industry, hence their machines will not play many of the compression types that you will download.
If you buy a cheapy, and make sure that it plays MPEG, Divx, AVI, etc, you will be able to just burn and watch without any hassle just as the file came down. Prices would be from about £25.
If you want any more advice just ask-Good Luck.